Does the incorporation of grit into the diet of Eisenia foetida affect feeding rate?

Laura Hicks and Rachael Young
March 19th, 2011

Abstract

Vermicomposting is the breakdown of organic material with the use of worms that is rapidly becoming a more frequently used form of composting. Past studies have suggested that the efficiency of breakdown would increase with the addition of inorganic particles such as grit, but there have been few experiments done to prove or disprove this suggestion. In this experiment we have treated a group of worms with grit and compared to it our control, which had no grit added to see how the breakdown of organic material (in this case apple pieces) was affected. After a set number of days we counted the number of apple pieces remaining in each group as well as the number of feces seen. From this experiment, it is suggested that the addition of grit showed no significance difference in the amount of organic material that had been broken down (p=0.05, t=2.04, df=44). These findings do not correlate with past studies suggesting that further research is needed to determine if the addition of grit to the diet of worms in a composter increases the rate at which food is broken down. Introduction

Vermicomposting is an eco-friendly composting solution that is becoming much more widespread due to its efficiency, cleanliness and relatively low cost (Morton, 2003). The process is fairly simple and involves the chemical breakdown of food with the use of worms such as Eisenia foetida, or more commonly known Red Wriggler worms. The result gives you beautiful enriched soil all whilst helping sustain the environment by preventing pollution. Although there have been few studies involving possible ways to increase the efficiency of vermicomposting, it is suggested that the addition of inorganic particles such as sand or grit will aid in the mechanical breakdown of food in the muscular gizzard (Firth, 2010). In this experiment we are looking to determine how the incorporation of grit into the diet of Eisenia foetida affects the digestive process. We want to know if it increases the feeding rate and therefore the amount of food being broken down in a composter over time. Our hypothesis states that grit does aid in the mechanical breakdown of food, which increases the rate at which the food is digested. This would result in a decrease in the amount of time it takes a given bolus of food to be eliminated and therefore increases the amount of food ingested in a given amount of time. If the hypothesis is true, we predict that worms that were given access to grit should ingest more than the ones that were not. Our results will help us determine if the addition of grit is an effective way to increase the efficiency of vermicomposting and if so, by what degree.

Materials and Methods

For this experiment, the worm species examined was the Eisenia feotida, the Red Wriggler obtained from a local vermicomposting supplier.
On 29/02/11, 17 worms were treated with Quikrete grit bought from Home Depot in Guelph, Canada. The grit had been rinsed for 1 hour with deionized water. 16 worms were not treated with grit. All worms were placed in Petri dishes lined with unbleached and eco-friendly paper towel. A circle was drawn in pencil in the center of the paper towel to indicate the feeding area. 5 mL of raw well water was then added to the dish. 10 pieces of Empire apple, obtained from Guelph Farmer’s Market, were also added to the Petri dish. These apples were sliced into 1mm thick sheets using a kitchen mandolin and cut into 1mm cubes with a sharp razor blade. If the worm in the Petri dish was marked for grit treatment, the grit was then added to the dish. The worms, after being weighed to 0.01 g, were also placed inside the dish. The lid of the Petri dish had the date, time, treatment and the weight of the worm written on it for record. During the